The present invention relates to the technical field of an image recording method and an image recording apparatus, and more particularly, to an image recording technique using a group of light source elements of two-dimensional arrangement.
Mainly used in a digital image exposure system utilized in various types of printers is a so-called laser beam scan exposure (raster scan) for two-dimensionally exposing a recording medium with a laser beam modulated in accordance with an image to be recorded by deflecting the laser beam in a main scanning direction while relatively moving the recording medium and an optical system in an auxiliary scanning direction perpendicular to the main scanning direction.
In contrast, in recent years, various types of digital image exposure systems have been proposed, which use two-dimensional spatial light modulators (2DSLM) such as a liquid crystal display (hereinafter, referred to as xe2x80x9cLCDxe2x80x9d) and the micro mirror array (hereinafter, referred to as xe2x80x9cMMAxe2x80x9d) such as, for example, a digital micromirror device (trade mark hereinafter referred to as xe2x80x9cDMDxe2x80x9d) manufactured by Texas Instruments Inc.), which are utilized as display devices in displays, monitors and so on. In the exposure systems, a recording medium is basically exposed by forming an image displayed by the two-dimensional spatial light modulator on the recording medium.
In particular, the MMA is advantageous in exposure at high speed because the MMA has a modulation speed (response speed) faster than that of the LCD and moreover utilizes light more efficiently than the LCD.
Digital exposure systems using the spatial light modulator are disclosed in, for example, U.S. Pat. No. 5,049,901 B, EP 0992350 Al B, U.S. Pat. No. 5,132,723 B and JP 2000-19662 B.
The digital exposure systems disclosed in these publications each relate to an image recording apparatus in which an image is formed on a spatial light modulator such as the MMA in the form of an image signal and the image signal is imaged on a recording medium for recording. In the digital exposure systems, the image on the spatial light modulator is moved in synchronism with the movement or the recording medium, which is moved in a main scanning direction so that the image can remain stationary on the recording medium. This operation enables image recording of high resolution by obtaining a small recording light spot from an extended light source, which has difficulty in narrowing the area.
The principle of an image recording method using the conventional spatial light modulator will be described with reference to FIGS. 12A to 12C. As shown in FIG. 12A, light impinges on a spatial light modulator 80 and is reflected by a mirror 80a, and the reflected light is imaged onto a recording medium 84 through an optical system such as a lens 82, etc. It is assumed that the recording medium 84 moves at a constant speed as shown by the arrow shown in FIG. 12A. In FIG. 12A, only the mirror 80a is activated and mirrors 80b and 80c are deactivated, and only the light reflected by the mirror 80a is imaged onto the recording medium 84.
Next, when the recording medium 84 slightly moves as shown in FIG. 12B, the mirror 80a in the spatial light modulator 80 is deactivated and only the mirror 80b is activated instead in synchronism with the movement of the recording medium 84, and the same point on the recording medium 84 as shown in FIG. 12A is exposed to the light reflected by the mirror 80b. 
Further, when the recording medium 84 moves as shown in FIG. 12C, only the mirror 80c in the spatial light modulator 80 is activated in synchronism with the movement of the recording medium 84 and images at the same position on the recording medium 84.
As described above, in the illustrated example, the spatial light modulator 80 changes image signaling (moves image data) three times so that each of the mirrors 80a, 80b and 80c exposes the recording medium 84 once, in total three times. As a result, the image is moved in synchronism with the movement of the recording medium 84 so as to remain stationary on the recording medium 84 in a main scan direction (a moving direction of the recording medium).
The (one-dimensional) movements of the mirrors concerning one pixel have been described in the above description. In reality, however, for instance, an image is recorded in the manner shown in FIG. 13 with this conventional image recording method. A recording medium 92 is wound around the external surface of a rotating drum 90, and image recording is performed by two-dimensionally exposing the recording medium 92 using an optical system that uses an image forming lens 96 and a two-dimensional spatial light modulator 94 (a group of two-dimensionally disposed light sources) irradiated with an illumination light flux. The rotating drum 90 rotates in the direction shown by the arrow T shown in FIG. 13. Also, an image is two-dimensionally recorded by setting the direction shown by the arrow M shown in FIG. 13 as the main scanning direction and setting the direction shown by the arrow S as the auxiliary scanning direction.
With the two-dimensional spatial light modulator 94, an image to be recorded onto the recording medium 92 is divided into small segments and image recording is performed for each unit of one segment (hereinafter, referred to as the xe2x80x9cframexe2x80x9d). Here, for ease of explanation, it is assumed that the two-dimensional spatial light modulator 94 includes 5xc3x9710 micromirrors. In this case, one frame is composed of 5xc3x9710 pixels. In FIG. 13, one frame of an image that is currently being recorded (exposed) is indicated by the reference symbol xe2x80x9cGxe2x80x9d and frames that have already been recorded are specified by the reference symbol xe2x80x9cG0xe2x80x9d. The rotating drum 90 continuously rotates at a constant speed in the direction of the arrow T, so that if the two-dimensional spatial light modulator 94 only exposes the frame G at the illustrated position, the recorded image of one frame G flows in accordance with the rotation of the rotating drum 90.
In view of this problem, as shown in FIGS. 14A to 14C, the image data on the two-dimensional spatial light modulator 94 is switched to have the recorded image of the frame G remain stationary on the recording medium 92. In more detail, while data shown in FIG. 14A is being sent to the two-dimensional spatial light modulator 94, the recording medium 92 moves downward in the drawing in accordance with the rotation of the rotating drum 90. Therefore, as shown in FIG. 14B, image data is switched so that the image data on the two-dimensional spatial light modulator 94 is shifted downward by one pixel (downward by one line) in its entirety in synchronism with the movement of the recording medium 92. When the recording medium 92 further moves downward by one pixel (by one line) in accordance with the rotation of the rotating drum 90, the image data is further switched as shown in FIG. 14C so that the image data on the two-dimensional spatial light modulator 94 is shifted again downward by one line in its entirety.
By switching the image data on the two-dimensional spatial modulator 94 in synchronism with the rotation of the rotating drum 90 in this manner, the recorded image can remain stationary on the recording medium 92 and image flow is prevented.
Following this, when the rotating drum 90 has rotated once and image recording for one line is finished, the optical system including the two-dimensional spatial light modulator 94 or the like is moved in the auxiliary scanning direction S by one frame (by ten pixels in this example) while the rotating drum 90 is making the next rotation. Then, image recording in the main scanning direction M is performed for the next line in the same manner as above during the still next rotation of the drum 90.
With the conventional image recording method described above, however, the image data of one frame held by the two-dimensional spatial light modulator 94 is switched (shifted) in synchronism with the rotation of the rotating drum 90. Also, when the recording of one line corresponding to one rotation of the rotating drum is finished and the next one line is to be recorded, the image data of one frame needs to be rewritten in its entirety. Accordingly, it is required to quickly rewrite modulation data for driving the two-dimensional spatial light modulator 94 many times, which imposes an enormous burden on an apparatus. Also, the image recording (of one line) in the main scanning direction and the moving of the optical system in the auxiliary scanning direction are repeatedly performed and image recording is performed only for one line while the drum is making two rotations. This causes a problem in that the scanning efficiency during image recording is reduced and the productivity is decreased. Also, the optical system is not continuously moved in the auxiliary scanning direction. That is, an operation for mechanically moving the optical system in the auxiliary scanning direction and an operation for stopping the movement are repeatedly performed. This causes a problem in that vibrations are generated in an apparatus and the durability and reliability of the apparatus are impaired.
Also, as shown in FIG. 15, with another conventional image recording method using a spatial light modulator, light from a light source (not shown) is reflected by a spatial light modulator 180 and recording light that carries an image is imaged onto a recording medium 184 through an image forming lens 182, thereby forming an image 186. The recording medium 184 moves at a constant speed as shown by the arrow A in this drawing. Accordingly, if only the image 186 is exposed for a long time, the image 186 flows in accordance with the movement of the recording medium 184. In view of this problem, the operation described below is performed in order to have the image 186 remain stationary on the recording medium 184 relatively.
Here, it is assumed that, as shown in FIG. 16 A, modulation data xe2x80x9cG0, G1, G2, G3, . . . , H0, H1, . . . , I0, . . . , J0, . . . , and K0, . . . xe2x80x9d exists on the spatial light modulator 180 and image recording is performed according to this modulation data. It is also assumed that the arrangement direction of pixels xe2x80x9cG0, H0, I0, J0, and K0xe2x80x9d (a column direction) coincides with the direction A in which the recording medium 184 moves, while the arrangement direction of pixels xe2x80x9cG0, G1, G2, G3, . . . xe2x80x9d (a row direction) is a direction perpendicular to the moving direction A of the recording medium 184. In this case, the recording medium 184 moves downward in FIG. 16A (in the direction of the arrow A), so that if the spatial light modulator 180 continuously holds this modulation data, an image on the recording medium 184 flows in the moving direction of the recording medium 184.
In view of this problem, as shown in FIG. 16B, when the recording medium 184 moves downward by one pixel, the modulation data is shifted downward by one line on the spatial light modulator 180. In more detail, the modulation data xe2x80x9cG0, G1, . . . xe2x80x9d on the first row is shifted to the second row and the modulation data on each of other rows is also shifted downward by one row. Then, the next modulation data xe2x80x9cF0, F1, F2, F3, . . . xe2x80x9d is newly sent to the first row.
When the recording medium 184 further moves downward by one pixel, the modulation data on each row is shifted downward by one line on the spatial light modulator 180 and new modulation data xe2x80x9cE0, E1, E2, . . . xe2x80x9d is introduced onto the first row, as shown in FIG. 16C.
By shifting the modulation data on the spatial light modulator in accordance with the movement of the recording medium in this manner, it becomes possible to have an image remain stationary on the recording medium relatively.
With this conventional image recording method, however, scanning is performed in a one-dimensional direction and an image can remain stationary only relatively to the movement in this one-dimensional direction. Therefore, if this method is applied to a case of two-dimensional scanning typified by an external surface cylinder type recording apparatus without any changes, for instance, there occurs a problem in that a recorded image is distorted like a parallelogram. This problem will be described below.
That is, as shown in FIG. 17, a recording medium 198 is wound around the external surface of a rotating drum 196 and light reflected by a spatial light modulator 190 is imaged onto the recording medium 198 through an image forming lens 192, thereby recording an image. Note that the rotating drum 196 rotates in the direction of the arrow T, the direction in which the rotating drum 196 rotates is set as the main scanning direction M and the direction of a rotational axis that is perpendicular to the direction M is set as the auxiliary scanning direction S. An optical system including the spatial light modulator 190, the image forming lens 192 and the like is mounted on an auxiliary scanning transport means 194 and is moved in the auxiliary scanning direction S.
While the rotating drum 196 is rotating once, the modulation data is controlled in the manner described above and an image 199a on the first column is recorded while shifting the modulation data on the spatial light modulator 190 in the one-dimensional direction. At this time, if a recording method called xe2x80x9cstep and repeatxe2x80x9d is used, while the image 199a on the first column is being recorded, the optical system is not moved in the auxiliary scanning direction. When the image recording for the first column is finished, the optical system is moved in the auxiliary scanning direction S during the next rotation of the rotating drum 196, and an image 199b on the second column is recorded during the next rotation of the rotating drum 196. With this recording method, image recording is performed only once (for one line) while the rotating drum is making two rotations, so that the recording efficiency is extremely low.
To solve this problem, image recording is successively performed by moving the optical system using the auxiliary scanning transport means 194 at a constant speed in the auxiliary scanning direction S. In this case, if modulation data is one-dimensionally shifted on the spatial light modulator 190 only in the main scanning direction M like in the cases of the conventional techniques, there occurs a problem in that a recorded image 199 is distorted like a parallelogram on the recording medium 198, as shown in FIG. 18.
In order to attain the first object described above, the first aspect of the present invention provides an image recording method in which when an image is recorded on one recording medium of a drum-shaped recording medium rotating at a first constant speed and a recording medium held on an external surface of a drum rotating at the first constant speed, the image being recorded by performing main scanning and exposure on the one recording medium with an optical system that uses a group of two-dimensionally disposed light source elements as well as by performing auxiliary scanning by moving the optical system in an auxiliary scanning direction that is substantially perpendicular to a main scanning direction, comprising the steps of:
deflecting light from the group of two-dimensionally disposed light source elements to move the image formed on the one recording medium in accordance with a movement of the one recording medium, thereby having the image remain stationary relatively to the one recording medium in the main scanning direction; moving the optical system at a second constant speed in the auxiliary scanning direction; and sequentially shifting modulation data of the group of two-dimensionally disposed light source elements in a direction opposite to a moving direction of the optical system in synchronism with a movement of the optical system in the auxiliary scanning direction, thereby having the image also remain stationary relatively to the one recording medium in the auxiliary scanning direction.
Preferably, when recording of the image of one frame, which is an image area to be recorded on the one recording medium by the group of two-dimensionally disposed light source elements by one operation, is finished and recording of the image of the next frame is performed, a deviation between the preceding frame and the next frame in the auxiliary scanning direction is an integral multiple of a recording pixel.
In order to attain the first object described above, the second aspect of the present invention provides an image recording apparatus, comprising: one recording medium of a drum-shaped recording medium rotating at a first constant speed and a recording medium held on an external surface of a drum rotating at the first constant speed; an optical system that uses a group of two-dimensionally disposed light source elements for exposing the one recording medium in a main scanning direction that is a first moving direction of the one recording medium; a modulation data generator that controls modulation data to be supplied to the group of two-dimensionally disposed light source elements; and an auxiliary scanning drive system that moves the optical system in an auxiliary scanning direction that is substantially perpendicular to the main scanning direction, wherein the optical system includes a deflector that deflects light from the group of two-dimensionally disposed light source elements, an image formed on the one recording medium is moved in accordance with a movement of the one recording medium by deflecting the light using the deflector, thereby having the image remain stationary relative to the one recording medium in the main scanning direction, and the auxiliary scanning drive system moves the optical system at a second constant speed in the auxiliary scanning direction and the modulation data generator sequentially shifts the modulation data of the group of two-dimensionally disposed light source elements in a direction opposite to a second moving direction of the optical system in synchronism with a movement of the optical system in the auxiliary scanning direction, thereby having the image also remain stationary relative to the one recording medium in the auxiliary scanning direction.
Preferably, when recording of the image of one frame, which is an image area to be recorded on the one recording medium by the group of two-dimensionally disposed light source elements by one operation, is switched to recording of the image of the next frame, the auxiliary scanning drive system drives the optical system in the auxiliary scanning direction so that a deviation between the preceding frame and the next frame in the auxiliary scanning direction becomes an integral multiple of a recording pixel.
In order to attain the second object described above, the third aspect of the present invention provides an image recording method in which when an image is recorded on a recording medium that is moved in a given direction at a constant speed relative to an optical system that uses a group of two-dimensionally disposed light source elements, the image being recorded by performing main scanning on the recording medium in the given direction with the optical system as well as by performing auxiliary scanning by moving the optical system relative to the recording medium in an auxiliary scanning direction that is substantially perpendicular to the main scanning direction, comprising steps of: shifting modulation data of the group of two-dimensionally disposed light source elements in a first moving direction of the recording medium on the group of two-dimensionally disposed light source elements in synchronism with a movement of the recording medium, thereby having the image remain stationary relative to the recording medium in the main scanning direction; and moving the optical system at a constant speed in the auxiliary scanning direction and shifting the modulation data on the group of two-dimensionally disposed light source elements in a direction opposite to a second moving direction of the optical system in accordance with an image recording position in the main scanning direction, thereby having the image also remain stationary in the relative relation to the recording medium in the auxiliary scanning direction and suppressing parallelogram-like distortion of the image recorded on the recording medium.
Preferably, a spatial light modulator that reflects an illumination light flux from a light source or allows the illumination light flux to pass through is used as the group of two-dimensionally disposed light source elements.
In order to attain the second object described above, the fourth aspect of the present invention provides an image recording apparatus, comprising: an optical system that uses a group of two-dimensionally disposed light source elements; a recording medium that moves in a given direction at a first constant speed relative to the optical system, an image being two-dimensionally recorded on the recording medium by performing main scanning in the given direction using the optical system and performing auxiliary scanning in a direction that is substantially perpendicular to the main scanning direction; a modulation data controller that controls modulation data to be supplied to the group of two-dimensionally disposed light source elements; and an auxiliary scanning drive system that moves the optical system in an auxiliary scanning direction at a second constant speed relative to the recording medium, wherein the modulation data is shifted in a first moving direction of the recording medium on the group of two-dimensionally disposed light source elements in synchronism with a movement of the recording medium, thereby having the image remain stationary relative to the recording medium in the main scanning direction, and the modulation data is shifted in a direction opposite to a second moving direction of the optical system on the group of two-dimensionally disposed light source elements in accordance with an image recording position in the main scanning direction, thereby having the image also remain stationary relatively to the recording medium in the auxiliary scanning direction and suppressing parallelogram-like distortion of the image recorded on the recording medium.
Preferably, a spatial light modulator that reflects an illumination light flux from a light source or allows the illumination light flux to pass through is used as the group of two-dimensionally disposed light source elements.